The invention relates to an arrangement for producing a vacuum in a motor vehicle system including a pump, which is connected, with its suction side, to a pneumatic power brake system for generating a vacuum in the power brake system.
It is known in practice that diesel engines are provided with vacuum pumps, which are connected with their suction side to a power brake system in order to produce the vacuum required for its operation. Air taken in from the latter is discharged to the surroundings. Vacuum pumps are needed because diesel engines are operated essentially without the throttle elements, which are provided in the intake ducts of spark-ignition engines. Therefore, in contrast to conventional spark-ignition engines, negative pressure, that is a vacuum, which can be used for operating the power brake systems, is not produced in the intake duct of a diesel engine.
In the case of conventional spark-ignition engines, the airflow to the engine cylinders is restricted in accordance with the amount of fuel injected by a throttle valve arranged in the intake duct. During partial-load operation of the spark-ignition engine, the throttle valve position is controlled to the extent that the cross-section constriction in the intake duct causes the cylinders to have a correspondingly smaller filling. This results in a negative pressure in the suction manifold downstream of the throttle valve. The negative pressure is used in spark-ignition engines for the evacuation of a vacuum reservoir for the power brake system.
Moreover, this vacuum is used in the prior art for the regeneration of a fuel-vapor adsorption system. The vacuum in the intake region is employed to generate a scavenging airflow through the activated-carbon canister.
To meet exhaust-emission regulations, warm-up procedures require that modern engines are driven with retarded ignition and increased idling speed. Also, the power consumed and the friction generated by additional equipment increase the load on the engine. As a result, the throttle valve has to be opened relatively wide during engine warm-up so that the vacuum available during this operating period is very small.
With further efficiency-increasing measures in the spark-ignition engine for a reduction of the consumption, the throttling means may even be fully replaced by controlled direct fuel injection with throttle-free load control and variable inlet valve operation. In these engine concepts, virtually no usable vacuum will be generated in the intake duct, i.e. the intake duct serves exclusively for the supply of air to the cylinders.
This means that, in the new engine concepts, either the throttle valve is omitted or it is largely ineffective for producing a vacuum.
As a result, a vacuum sufficient for operating power brake systems can no longer be generated in the intake duct.
For this reason, even in motor vehicles having spark-ignition engines, the vacuum is produced sometimes by providing a suction pump as it is done in connection with diesel engines, in order to permit operation of the power brake system. Systems of this type are disclosed in DE-A 2 347 701 and WO 93/11983.
However, it has so far not been possible in any of the above-described systems to satisfactorily use the pump in connection with the fuel-vapor-retaining systems arranged in motor vehicles.
The object of the present invention is to provide an arrangement with which a power brake system and a fuel-retaining (fuel vapor adsorption) system can be operated by a vacuum generated by a pump wherein, at the same time, the fuel consumption is reduced and the amount of pollutants emitted are minimized.
In an arrangement for producing a vacuum in a motor vehicle system including an internal combustion engine with an air intake system, a vacuum-operated power brake system for braking the vehicle and a fuel vapor adsorption system for collecting fuel vapors, a vacuum pump is provided which has a suction side in communication selectively with the vacuum operated power brake system and the fuel vapor adsorption system and a discharge side in communication with the air intake system of the internal combustion engine.
With the arrangement according to the invention, a vacuum can be produced which is sufficient and always available for the operation of a power brake system and which is available over the entire operating range of an internal combustion engine. Moreover, efficient regeneration of a fuel-vapor-retaining system is made possible.
Such a fuel-vapor-adsorption system can also be operated in the high load range or in the full load range of the engine. During high load operation, a high air mass flow is supplied to the engine so that a very efficient regeneration is possible. At the same time, the conversion of the fuel vapors in the engine is particularly effective because of better engine charge conditions. Also, with conventional throttle-controlled engines an insufficient vacuum is generated during high load engine operation for proper braking operation or for a proper regeneration of the fuel vapor adsorber.
The activation of the power-brake system and the regeneration of the fuel vapor adsorber system can be achieved with a single pump. The air flow or air/fuel-vapor flow generated by the pump is introduced into the intake system of the internal combustion engine.
Further advantages and embodiments of the invention will become apparent from the following description of the invention based on the accompanying drawing.